A series of relatively rigid molecules, from the endoethenooripavine family of opioids known to bind to opioid receptors from rat brain cerebrum homogenates and neuroblastoma-glioma hydride cells, were converted to ligands potentially capable of irreversible interaction with those receptors. Two other compounds, besides our initial ligand in that series, have now been found to act as an irreversible binding ligand for the delta and mu opioid receptors.